1. Field of the Invention
The invention relates to a belt brake for a safety belt serving to protect occupants in a vehicle, which belt can be wound onto and unwound from a belt drum mounted rotationally about a belt shaft. Furthermore, a method is described for locking a safety belt serving to protect occupants in a vehicle.
2. Description of the Prior Art
Modern safety belt systems generally comprise a plurality of mechanically passively working systems which are intended to guarantee that the vehicle occupants are subjected to the lowest possible loads during an accident, and also have, if possible, no contact with the vehicle interior, not even with the parts which may penetrate the passenger compartment due to the impact. Almost all devices of prior art for braking or locking safety belts provide passively acting closing devices which, can be activated suddenly, independently of the accident situation and the vehicle occupants to be protected from injuries and, in particular, independently of their weight and size. Adaptive systems which guarantee braking of the safety belt, independently of the accident seat and passengers, cannot be achieved or can only be achieved at a high design cost.
In addition to the devices which are intrinsically known for belt braking only and which, in particular, are intended to prevent further unwinding of the belt from the belt drum, intelligent belt tightening systems are known which are integrated in entire sensor-supported vehicle systems, and can be actuated situation-dependently on the basis of data recorded by the sensors. For example, the ignition times of airbags and also the triggering of belt tightening systems are also influenced by these data. Reversibly operating belt tighteners force the vehicle occupants into an optimum sitting position, in which the moments of force acting on the vehicle occupants during the collision are to be kept within a largely physiologically tolerable limit. Such reversibly operating belt tighteners of prior art use electric motor drives to tighten the belt in a predetermined manner. Such a belt tightener is disclosed, for example, in DE 199 27 731 C2. Even if it is merely suspected that a collision is imminent, suitable signals activating the belt tighteners can be emitted by suitable evaluation of the data deriving from so-called pre-crash sensors in the vehicle. In this manner the distance which the vehicle occupants slide forward shortly before a collision can be reduced from up to 150 mm to 50 mm, which represents a quite considerable safety potential. Repeated tightening of the safety belts may also be advantageous if the vehicle overturns several times or if there are several impacts. However, the belt tightening system described in the above-mentioned patent specification has a multiplicity of individual components whose susceptibility influences the reliability of the entire system. Thus the acceleration and braking moment generated by the electric motor is transferred by means of a planetary gear to the belt shaft onto which the belt is wound or from which it is unwound.